Certain fungal pathogens are known to produce host-specific toxins (HSTs) that determine their host range and contribute to their virulence or pathogenicity. Recently, technology for breeding disease-resistant genotypes from susceptible plants by using HSTs is relatively prevalent. In many plants, somatic mutations generated through the growth of tissues or cells in culture release novel disease resistance characters, and HSTs are used to select in vitro for such characters.We found that Alternaria brassicicola, cucumber pathotype and tomato pathotype of Corynespora cassiicola, and Stemphylium vesicarium produce new HSTs named AB-, CCC-, CCT- and SV-toxins, respectively. AB-toxin was a protein and estimated to be 35 kDa, and CCT-toxin was a cyclic peptide with molecular weight of 2,780.CCT-toxin of C.cassiicola tomato pathotype was used for production of disease-resistant tomato. Tomato calli with green spots which have a high regeneration frequency were induced from hypocotyls and transferred to MS medium containing CCT-toxin. Although almost all calli became brown, some calli continued to survive even after incubation for 3 weeks. However, the toxin-tolerant calli lost ability to regenerate. On the other hand, A.alternata tomato pathotype produces a HST (AAL-toxin). Recently, the ESP1 which metabolizes AAL-toxin was cloned from black yeast Exophilia spinifera. Therefore, production of disease-resistant tomato by detoxification of AAL-toxin in ESP1-transgenic tomato was attempted. Transformation of ESP1 in tomato was performed by Agrobacterium tumefaciens containing binary vector with ESP1. However, transformants have not yet been obtained.